Doc patch: provide a pointer to where the list of --with-PROG values is.  Fixes #1512.

(cherry picked from commit 372ee37754e7f34bd2fda06bf27e4d192f3c4e0a)
Add a quickstart to the development chapter of the user guide

It covers using cabal init and the basic steps for building from there.

(cherry picked from commit afe31a8880fb8c5da2429e75f5f10768dbfcee49)
Rewrite and extend several parts of the user guide introduction

Introduce cabal-install much earlier. Give more of a basic intro.

(cherry picked from commit 7ec473a75c8be86722ba3ed13ac6d0579ceb9887)
Try using a contents within each user guide chapter

Currently we have a somewhat hard-to-maintain contents just in the
introduction. This cuts that initial contents down to just link to
the chapters (plus sections within the intro), and then use an
automatically generated table of contents in the other chapters.

Also tweak the CSS because pandoc's TOC feature turns all section
headings into links and that changes the visual appearance. Use the
CSS to make it look the same as before.

(cherry picked from commit 9ecb30d4dbccb07eaf342aab0dd525ec4c9cbbd0)
Limit the length of lines in the user guide html to be readable

(cherry picked from commit 1c183eb9c2691ea6e8bd8d14aa8cd80775626533)
Add a user guide section on package concepts

(cherry picked from commit abed563e17b671793d5d9999fbdbc07c87c57749)